As a critical part of the drilled shaft quality control (FHWA, 1999), inspecting the bottom cleanliness of drilled shafts has always been challenging to contractors, engineers, and field inspectors, especially in the situation of the wet construction method, when direct visual inspections are impossible. Even with the dry construction method, inspectors have been reluctant to inspect the bottom visually due to safety concerns. On the other hand, most federal and local agencies, such as states' department of transportation and city building authorities specify that drilled shafts be inspected for bottom cleanliness. Typically, a minimum of 50 percent of the base of each shaft should have less than 0.5 inch of sediment at the time of concrete placement, and the maximum depth of sediment or any debris at any place on the base of the shaft is not allowed to exceed 1.5 inches. Conscientious cleaning of the bottom of drilled shafts has been proven by loads tests to be necessary for suitable load transfer in end bearing.
Currently, the Shaft Inspection Device (SID) or Miniature Shaft Inspection Device (Min-SID) are the only devices recognized as being relatively accurate to measure the drilled shaft bottom sediment without an inspector's direct measurement in the hole.
SID was developed in the early 1980s by Schmertmann and Crapps, Inc. The SID comprises a television camera sealed inside a water-tight jacket and is used for inspecting both dry and wet excavations. The concept of the SID was derived from an Australian drilled shaft inspection device originally developed by Dr. Jim Holden of the Country Roads Board. SID is a heavy (over 1000 lb) and large equipment. The operation is relatively expensive and time consuming.
Mini-SID was introduced around 1998 with much lighter weight and easier operation procedures. However, it still involved the operations of specifically trained personnel and relatively time consuming test procedures.
Given these reasons, a portable drilled shaft inspection device with improved efficiency is desired. The device should have the following key points:
1. Simple Operating Process
2. Very Efficient
3. High Reliability